1. Field of the Invention
The present invention relates to techniques for preventing exposure of asbestos fibers, and melting and solidifying asbestos fibers. More specifically, according to the techniques, the exposure of the fibrous dust of the asbestos from an asbestos-containing material can be prevented at the time of dismantling already-constructed asbestos-containing materials (building materials, products, etc.), at the time of collecting and transporting the dismantled asbestos-containing materials, and at the time of melt treating the collected asbestos-containing material, and also the asbestos-containing materials can be melt treated at temperatures as low as 1,500° C. or less.
2. Description of the Related Art
Conventionally, products using asbestos are excellent in heat resistant properties, chemical resistant properties, and electrical insulation properties. Accordingly, the products using asbestos are used for various applications such as fire resistive covering materials including building materials, brake pads, etc. However, it is pointed out that when a human inhales exposed fibrous dust of the asbestos, they may suffer from serious diseases such as asbestosis pulmonum, lung cancer, or malignant mesothelioma, though the asbestos has the excellent physical and chemical properties.
At present, asbestos-containing industrial wastes are buried in final disposal sites. However, there is a limitation on the amount of the asbestos-containing industrial wastes capable of being disposed by burying, because the burying sites etc. are restricted. There have been proposed methods of preventing the exposure of the asbestos fibers from the asbestos-containing industrial wastes or methods of treating asbestos-containing industrial wastes into harmless materials.
For example, Japanese Patent Application Laid-open No. 62-237984 discloses a method of melt treating and solidifying asbestos-containing industrial wastes involving adding a melting aid such as an oxidized compound.
Japanese Patent Published Application No. 05-012994 discloses a method of treating asbestos-containing industrial wastes into harmless material involving treating the asbestos-containing industrial wastes with phosphoric acid, and then adding an alkali agent such as calcium carbonate.
Japanese Patent Application Laid-open No. 09-110514 discloses a method involving impregnating water into asbestos-containing wastes, adding sodium silicate or potassium silicate thereto to form a gel layer of an alkali silicate on the surfaces of fibers, and calcining and sintering at 1,000 to 1,200° C.
Japanese Patent Application Laid-open No. 2006-063299 discloses a method of preventing exposure of fibrous dust of asbestos involving impregnating a sealant at the time of dismantling asbestos building materials, or the like.
Japanese Patent Application Laid-open No. 2006-043620 discloses a method of melt treating asbestos-containing wastes involving impregnating a sealant into asbestos attached to a metal structure, and then packing the same in a storing container to be melt treated.
However, the methods disclosed in the above-mentioned documents have the following problems.
Japanese Patent Application Laid-open No. 62-237984 discloses a method involving crushing an asbestos waste material using a mixer, and then supplying a melting aid from a hopper for the purpose of melting and hardening the asbestos-containing waste material in such a manner that asbestos is vitrified or forms a harmless crystal at the time of melting. However, in this method, it is assumed that a melting aid is added to the asbestos-containing waste material in a closed space (mixer). Thus, it is not required for the selected melting aid to have an effect of preventing the exposure of the fibrous dust of the asbestos, and it is unclear whether such a melting aid has an effect of preventing the exposure of the fibrous dust of the asbestos.
Japanese Patent Published Application No. 05-012994 discloses a method involving mixing, by stirring, an asbestos-containing waste material and an aqueous phosphoric acid solution, and the like for granulating, followed by calcination, and further adding an alkali agent such as calcium carbonate, followed by calcination to form a granular material for the purpose of destroying a fiber structure of asbestos. However, in this method, it is assumed that wet blending is performed, which is clear from the fact that asbestos is mixed with an aqueous phosphoric acid solution, or the like, stirred, and granulated. In view of this, it is not required for such a chemical agent to have an effect of preventing the exposure of the fibrous dust of the asbestos, and it is unclear whether such a chemical agent has an effect of preventing the exposure of the fibrous dust of the asbestos.
In the method as described in Japanese Patent Application Laid-open No. 09-110514 involving adding sodium silicate or potassium silicate, and then calcinating and sintering, an asbestos-containing waste material is crushed and the resultant is mixed and kneaded with sodium silicate, or the like, for the purpose of treating the asbestos-containing industrial waste into harmless material for effective use. However, in this method, it is assumed that an asbestos-containing waste material is milled, and water is blended with sodium silicate etc., for curing. In view of this, the chemical agent is required to function as a curing agent, and is not required to have an effect of preventing the exposure of the fibrous dust of the asbestos. It is unclear whether the chemical agent has an effect of preventing the exposure of the fibrous dust of the asbestos.
In the method as disclosed in Japanese Patent Application Laid-open No. 2006-063299 involving preventing the exposure of the fibrous dust of the asbestos by impregnating a sealant, a silicon compound containing silicone and alkoxy silane is impregnated into the surface of an asbestos-containing material, followed by hardening, thereby preventing the exposure of the fibrous dust of the asbestos. However, since the method aims to prevent the exposure of the fibrous dust of the asbestos over a long period of time, a sealant is required to merely function as a exposure preventing agent. It is unclear whether an asbestos material can be melted at low temperatures using such a chemical agent.
In the method disclosed in Japanese Patent Application Laid-open No. 2006-043620 involving impregnating a sealant into asbestos attached to a metal structure, and packing the resultant into a storing container, the sealant is sprayed merely to prevent the exposure of the fibrous dust of the asbestos. Thus, it is unclear whether an asbestos-containing material can be melted at low temperatures using such a chemical agent.
The inventors of the present invention have carried out various studies and developments in view of the above-mentioned problems, and as a result, have found that the use of lithium silicate as a exposure preventing agent makes it possible to prevent the exposure of the fibrous dust of the asbestos and to melt an asbestos-containing material at temperatures as low as 1,500° C. or less, at the time of dismantling an already constructed asbestos-containing material, at the time of collecting and transporting the dismantled asbestos-containing material, and at the time of melting the collected asbestos-containing material. Based on this finding, the present invention has been accomplished.